The upper lumbar and lower thoracic spine is the site of numerous spinal abnormalities and injuries. These may include trauma such as burst fractures, infection such as Pott's disease and other conditions such as tumors, post traumatic deformities, spinal cord compression, scoliosis and congenital deformities. Surgical approaches may be either posterior or anterior for many of these problems. In many cases the surgical approach is dictated by the pathology. In other cases, such as trauma to the thoracolumbar junction, the surgeon's preference and experience may allow either posterior or anterior approaches.
Anterior procedures at the thoracolumbar junction have traditionally been approached using one of several combined thoracic and retroperitoneal exposures. The classic approach usually involves a tenth rib thoracotomy. In this approach, an incision is made directly over the tenth rib and is carried caudally along the boarder of the rectus abdominus muscle. This is followed by excision of that rib and entry into the chest cavity. The lung is either packed away or deflated using a double lumen endotracheal tube. The diaphragm is taken down at its periphery to allow access to the retroperitoneal space which is then developed with blunt dissection. This technique was popularized by Hodgson and Stock and thoroughly described in Moe's Textbook of Scoliosis.
Other open approaches include extrapleural rib and flank approaches. In the eleventh rib approach, an incision over the eleventh rib is followed by a retropleural approach to the spine. This approach spares the chest cavity from invasion. The twelfth rib approach is very similar. The twelfth rib is removed followed by a retroperitoneal exposure of the spine. Similarly, the flank approach may be used to expose the retroperitoneal space and then extend cephalad under the diaphragm. Each of these approaches may be chosen for its utility in achieving exposure for the patient's particular problem, the specific spinal levels to be operated and the surgeon's experience.
Following these various surgical approaches, numerous anterior systems have been employed including dual rod systems and plate systems such as disclosed in U.S. Pat. Nos. 5,108,395 and 5,702,395. These instrumentation systems rely on reconstituting the load bearing function of the anterior column by insertion of a bone graft or cage spanning a fractured segment after removing the fractured vertebra and the adjacent two discs. Stability is achieved typically with two screws in adjacent vertebra spanned by a longitudinal plate or two rods. The advantages of the anterior approach include restoration of anterior load bearing capability at the time of surgery and fusion of only the levels adjacent to the incompetent vertebra.
Each of the open approaches require significant exposure of several levels of the spine, causing a great degree of approach related morbidity. The degree of morbidity increases as the number of exposed spinal levels expands. Morbidity includes post operative incision pain, pain associated with rib removal, risks to the intercostal vessels and intercostal neuritis. Substantially longer scars also cause concern for cosmesis in some patients.
Spinal conditions have also been treated posteriorly with Harrington distraction instrumentation. The Harrington instrumentation includes hooks and rods to effect and maintain corrected positioning of vertebrae during the fusion process. The rods are used to apply forces to straighten the spine and to maintain the corrected configuration until the vertebrae are fused. Typically, fusion is attempted from several levels above the pathology site to several levels below. The exact number of levels fused depends on the character of the fracture and the surgeon's training and varies from three to six vertebra. When following a "rod long, fuse short" philosophy, many surgeons have recommended removing the rods after the fusion has healed. Harrington type instrumentation is disclosed in U.S. Pat. Nos. 4,369,769 and 4,386,603, for example.
Many surgeons debate the biomechanical and clinical advantages and disadvantages of posterior versus anterior treatment of fractures and other conditions. One reason anterior approaches may be preferred is that they allow surgeons to address thoracolumbar fractures directly at the site of greatest biomechanical advantage. First, the material causing the injury usually lies anteriorly and is therefore most easily removed from this aspect. Also, the motor tracts lie predominantly on the anterior aspect of the spinal cord and may more easily be restored from this approach. Finally, it is generally agreed that decompression of the neural tissue to facilitate a patient's recovery from acute traumatic spinal cord injuries is best accomplished through an anterior approach to the spine.
The anterior approach would provide a clear advantage if approach related morbidity from the anterior approach to the thoracolumbar spine could be reduced through minimally invasive endoscopic techniques. An endoscopic approach to the thoracolumbar junction would also allow minimally invasive access for other procedures such as anterior releases for scoliosis, anterior instrumentation for scoliosis, spinal cord decompression for tumor or infection, biopsies, and repair of post traumatic kyphosis.
In spite of the potential benefits of such endoscopic techniques, challenges remain. In many cases, distraction or compression is required to correctly reposition the spinal deformity after the spinal cord has been decompressed. Typically, portions of the anterior vertebral column (i.e., the vertebral body) are removed to relieve pressure on the anterior portion of the spinal cord. Bone grafting and fusion is then required to achieve a stable correction. These requirements have not lent themselves to the confines of an endoscopic approach using prior art technology. Therefore, a need has remained for endoscopic devices and techniques for curvature correction, spinal canal decompression, anterior fusion, and internal fixation.